Power transmission

ABSTRACT

A power assisted directional control valve for hydraulic power systems has a sliding spool actuated by a differential piston. A follow-up valve is telescoped within the spool and controls the admission and release of pilot pressure fluid to and from the large side of the actuating piston. To enable the main spool to be shifted in the event of failure of the pilot pressure supply, an auxiliary pilot valve is opened upon overtravel of the normal pilot valve and admits pressure fluid trapped by the main spool to both sides of the actuating piston.

United States Patent Farrell [4 June 13, 1972 [54] POWER TRANSMISSION 2,685,794 8/1954 Hall et a1 ..91/376 x [72] Inventor: Robe G. Fm", Roy a1 Oak, Mich 2,906,246 9/ 1959 D1 Tlrro et a1 ..91/6

[ 73] Assignee: Sperry Rand Corporation, Troy, Mich. Primary Examiner-M. Cary Nelson Assistant Examiner--Robert J. Miller F 18 971 [22] Flled eb l Attorney-Van Meter and George [21] Appl. No.: 116,375

[57] ABSTRACT [52] US. Cl ..l37/625.6, 91/6, 91/416, A power assisted directional comm] valve f hydraulic power 91/417 systems has a sliding spool actuated by a differential piston. A 5 l Int. Cl ..F 15b 15/17 follow up valve is telescoped within the Spool and controls the [58] Field Of Search ..-.137/625.63, 625.6, 625.64, admission and release of pilot pressure fl to and from the 137/6252; 91/417 6 large side of the actuating piston. To enable the main spool to be shifted in the event of failure of the pilot pressure supply, [56] References cued an auxiliary pilot valve is opened upon overtravel of the nor- UNITED STATES PATENTS mal pilot valve and admits pressure fluid trapped by the main spool to both sides of the actuating piston. 638,489 12/1899 Albree ..91/417 R X 2,363,l l l 1 H1944 Bennett l 37/625.64 3 Claims, 2 Drawing Figures POWER TRANSMISSION With the construction of larger and larger mobile material handling machinery, the hydraulic power systems which they employ require larger and larger directional valves for controlling the flow of pressure fluid to the hydraulic actuators which operate their buckets, blades and similar material handling members. With the larger size valves, it becomes uneconomical to position the valves adjacent the operator and lead the numerous large size conduits to and from that position. It is more economical to locate the valves for convenience of plumbing and to provide mechanical actuating means between the operators station and the valve. These mechanical actuators, however, require rather heavy construction and oftentimes must be lead through devious paths through the machine, resulting in lost motion and the lack of precision in correspondence between the position of the operators handle and the position of the valve spool ultimately operated. In addition, the manual effort required to shift the large size hydraulic valves becomes somewhat high, further increasing the difficulty of achieving reliable control of a large valve from a distant operator's position.

These problems are alieviated by the use of power-assist devices using a follow-up servomotor operating on pilot pressure fluid supplied from a convenient source. These devices, however, become inoperative upon loss of pilot pressure, such as occurs upon engine failure in a typical construction machine; and should the load device be at the moment in an elevated position, there is no way to shift the main spool to enable the load to be lowered.

It is an object of the present invention to provide an improved power-assist directional control valve in which an auxiliary pilot valve may be actuated upon overtravel of the normal pilot valve for the purpose of admitting fluid trapped by the main spool to the actuating piston of the main spool.

This object is achieved by the invention which consists in a remotely controlled directional valve comprising a main body, a main spool slidable in the body, porting in the body and grooving on the spool to direct fluid flow forwardly and reversely and to terminate flow to and from a work device, a centering spring for the main spool, means forming an actuating piston for the main spool and having large and small effective areas on its opposing faces, a follow-up pilot valve for ad mitting and releasing pressure fluid to and from the large side of the actuating piston, and an auxiliary pilot valve normally inoperative and responsive to overtravel of the follow-up pilot valve for admitting pressure fluid trapped by the main valve to the actuating piston in the event of failure of the main spool to shift when the follow-up pilot valve is shifted.

IN THE DRAWINGS FIG. 1 is a longitudinal sectional view of a valve incorporating a preferred form of the present invention.

FIG. 2 is an enlarged fragmentary view of a portion of FIG. 1.

As illustrated in FIG. 1, the main valve comprises a body and a sliding spool 12 which may be of any convenient form for controlling hydraulic power between a pressure supply and a work device. Such valves may have a plurality of ports such as l4, l5, l7 and 19 in the body and of grooves such as 16 and 21 in the spool. The ports 14 and 19 may communicate with the tank return passages in the hydraulic power system and the ports 15 and 17 communicate with the reversible motor passageways in the valve. The valve will usually also contain other ports and grooves, not illustrated, but which are well known in the art. A centering spring assembly 18, of conventional form, holds the valve in its center or neutral position. When the spool 12 is shifted to one side or the other of center position against the bias of the spring 18, flow to and from the work device will be initiated in either forward or reverse sense respectively. These features are illustrative of the many well known types of hydraulic directional control valves.

The spool 12 is provided with a differential actuating piston 20, the left side of which has an effective area substantially pilot housing 22 is attached to the right end of the body 10 by suitable bolts and has a cylindrical bore 26 within which the piston 20 reciprocates. Sliding seals at 28 and 30 are provided for the spool 12 and the piston 20 respectively. The main spool 12 has a pilot valve bore 32 which communicates near its left end through radial bores 34 with the tank return port 14 of the :main body 10. Near its right-hand end, the bore 32 communicates by passages 36 with the space at the small area side of the piston 20 which is constantly exposed to pilot fluid pressure, as will later be described. Slidable in the bore 32 is a pilot valve spool 38 having lands 40 and 42 which, in the neutral position illustrated, just close off the radial passages 34 and 36. The spool 38 has an internal passage 44 which connects its left end face with the space at the right of the differential piston 20. A pin 46 is pressed in the spool 38 and cooperates: with a groove 48 in the main spool 12 to limit the motion of the pilot valve relative to the main spool. The lands 40 and 42 control the admission and exhaust of pilot pressure fluid to and from the large area side of piston 20, causing the spool 12 to follow-up the displacements of the stem 38.

The pilot valve spool 38 has a groove 50 which receives a rotary actuator comprising a lever 52 secured to a rotary shaft 54. The shaft 54 projects through the wall of the pilot body 22 and may be connected to any desired operating mechanism, such as an external operating lever, to be moved by a suitable linkage connecting with the operators handle. The top of the pilot body 22 is closed by a cap member 60 having a fluid terminal 64 for connection to a suitable source of pilot pressure fluid. Passages 66 in the cap 60 and the pilot body 22 supply such pressure fluid to the bore 26 at the left side of the differential piston 20 and also through radial passages 36 to the pilot valve itself. The cap 60 also contains a detent plunger 70 connected to the lever 52 and a spring centering mechanism 82. A detent release solenoid is indicated at 62.

- The main spool 12 also contains a bore 84 coaxial with the pilot valve bore 32 and having an extension 86 which communicates by a radial port 88 with the groove 21 on the main spool. Secured within the bore 84 by a pin 90 is an auxiliary pilot valve body 92 having a central bore 94 which slidably receives an auxiliary pilot spool 96. The body 92 has ports 98 which are normally closed by the auxiliary pilot spool. A spring 100 urges the pilot spool to its right-hand position against the retaining ring 102, as illustrated in HQ 2. A washer 104 abuts a shoulder in the bore 94 of the body 92 and serves as a check valve opening to flow from the ports 98 toward the right-hand end of the auxiliary pilot valve. A pin 106 at the right-hand end of the auxiliary pilot spool 96 serves as an abutment through which the main pilot spool 38 may shift the auxiliary pilot spool to the left upon overtravel of the main pilot spool.

The main spool 12 is normally shifted by pilot fluid pressure acting on the differential piston 20 and under control of the follow-up pilot valve 38. In the event, however, that there is a loss of pilot pressure due either to engine failure or breakages of the pilot supply line, it then becomes impossible to shift the main spool away from its spring centered position by the action of the pilot valve 38 alone. If the load device, such as a filled loader bucket, should be in an elevated position upon such an occurrence, the weight of the bucket will create a fluid pressure within the motor port 17 because the fluid in this port is trapped by the groove 21. When the operator shifts the control handle to lower the bucket, this shifts the follow up pilot spool 38, opening the large side of piston 20 to pilot pressure through passages 36. Since there is no pilot pressure, the main spool will not move. However, upon further travel of the main pilot valve 38, the auxiliary pilot valve is shifted to the left by contact with the operating pin 106. This opens the ports 98 and allows the trapped fluid pressure to pass through the check valve washer 104 and through the hollow interior 44 of the follow-up pilot valve to both sides of the actuating piston 20. Thus, the main spool 12 will be shifted to the left, opening the port 17 to the tank port 19 and allowing the loaded bucket to descend.

half that of the right side. A

I claim:

1. A remotely controlled directional valve comprising a main body, a main spool slidable in the body, porting in the body and grooving on the spool to direct fluid flow forwardly and reversely and to terminate flow to and from a work device, a centering spring for the main spool, means forming an actuating piston for the main spool and having large and small effective areas on its opposing faces, a follow-up pilot valve for admitting and releasing pressure fluid to and from the large side of the actuating piston, and an auxiliary pilot valve normally inoperative and responsive to overtravel of the follow-up pilot valve for admitting pressure fluid trapped by the main valve to the actuating piston, in the event of failure of the main spool to shift when the follow-up pilot valve is shifted.

2. A valve as defined in claim 1 wherein the auxiliary pilot valve includes a check valve opening to flow toward the actuating piston.

3. A valve as defined in claim 1 wherein the auxiliary pilot valve is within the main spool and coaxial with the follow-up pilot valve.

* i I i 

1. A remotely controlled directional valve comprising a main body, a main spool slidable in the body, porting in the body and grooving on the spool to direct fluid flow forwardly and reversely and to terminate flow to and from a work device, a centering spring for the main spool, means forming an actuating piston for the main spool and having large and small effective areas on its opposing faces, a follow-up pilot valve for admitting and releasing pressure fluid to and from the large side of the actuating piston, and an auxiliary pilot valve normally inoperative and responsive to overtravel of the follow-up pilot valve for admitting pressure fluid trapped by the main valve to the actuating piston, in the event of failure of the main spool to shift when the follow-up pilot valve is shifted.
 2. A valve as defined in claim 1 wherein the auxiliary pilot valve includes a check valve opening to flow toward the actuating piston.
 3. A valve as defined in claim 1 wherein the auxiliary pilot valve is within the main spool and coaxial with the follow-up pilot valve. 